<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>固定定位</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        .box{
            height: 1500px;
            background: yellow;
        }
        .ad{
            width: 100px;
            height: 200px;
            background: red;
            position: fixed;
            right: 0;
            bottom: 100px;
        }
    </style>
</head>
<body>
    <div class="box">

    </div>
    <div class="ad">

    </div>
</body>
</html>